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hybrid: /dev/pci -- a driver can live outside the kernel now

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docs/plan/hybrid.md mechanisms 2 and 4: MMIO and DMA to a process.

A process can enumerate the bus, claim a device exclusively, map its BARs and
get memory the device can be pointed at. Proven end to end against an e1000e
-- the exact device class we cannot drive and would want a foreign driver for:

    device 7: 8086:10d3 (network)
      claimed
      BAR0 at 0x81060000, 128 KB
      regs[0..3] = 0x00140261 0x00000000 0x00080283 0x00000000
      MMIO reaches the device
      DMA 8 KB at virtual 0x40001000, physical 0x3f8eb000

Those are the e1000e's CTRL and STATUS with full-duplex and link-up set, which
is how you tell a real mapping from one reading 0xFFFFFFFF off an unmapped
address. Claiming a device the kernel drives is refused -- two writers of one
register set looks like hardware that has started lying -- and everything a
process held is released when it exits, because a driver that crashed must not
keep its hardware away from its replacement.

mmap's offset is the BAR's physical address, checked against the BARs of
devices *this process has claimed*. Without that check the device is /dev/mem
with extra steps and a process could map the kernel's own memory. Mappings are
write-through: a cached write to a doorbell arrives whenever the cache feels
like it, which from a driver's side is indistinguishable from hardware that
ignores you.

The interface is about PCI devices, not about any driver model, and its first
users will be SchOS's own drivers when virtio-gpu is evicted. That ordering is
the design rather than an accident: an interface whose first consumers are
native drivers is a general mechanism something foreign can use later, instead
of a hole shaped like something foreign.

Also: PROT_* and MAP_* moved to include/posix.h. They were defined only in
sys_mem.c, so cmd/fbinfo carried a private copy and this wanted a third --
two copies of a number the kernel compares against, where a mismatch shows up
as a mapping with the wrong permissions rather than an error.

No IOMMU, so this isolates a driver against its own bugs and not against its
own DMA. The plan says so at length and it is still true.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VQ7Qx8E1q1M1bbCq8QLHS2
This commit is contained in:
Nexoniarz 2026-09-13 15:34:28 +02:00
commit 24f79194ab
14 changed files with 678 additions and 11 deletions
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4
Makefile
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@ -25,7 +25,7 @@ KERN_CORE = $(addprefix $(BUILD)/kernel/core/, \
KERN_DEV = $(addprefix $(BUILD)/kernel/dev/, \
bio.o cdev.o device.o disk.o fb.o ide.o input.o irq.o kbd.o mouse.o \
pci.o text.o ttf.o uart.o gfx.o vt.o ramdisk.o procfs.o)
pci.o pciuser.o text.o ttf.o uart.o gfx.o vt.o ramdisk.o procfs.o)
# Drivers for hardware that has to be *found* rather than assumed. Anything
# discovered by walking a bus belongs here; the fixed-address legacy devices
@ -107,7 +107,7 @@ KERN_NOENTRY = $(filter-out $(BUILD)/kernel/arch/x86_64/entry.o, $(KERNOBJS))
# Third-party software does NOT go here — see ports/.
# -----------------------------------------------------------------------
ULIB = $(addprefix $(BUILD)/lib/, start.o glue.o usys.o)
CMDS = init schinit schinitd fbinfo shmtest socktest inputtest nettest reflink schattr ping chvt
CMDS = init schinit schinitd fbinfo shmtest socktest inputtest nettest reflink schattr ping chvt pcitest
CMDBINS = $(addprefix $(BUILD)/cmd/, $(CMDS))
# -----------------------------------------------------------------------